BACICGROUND
AND OBJECTS R . SORRIS SHREVE P u r d u e Uni\ emit), Lafajette. Irtd.
HIS is the third in a consecutive series of symposia (6) and the fourth on the subject of unit processes. The first symposium was conducted under the chairmanship of D. B. Keyes a t the Denver meeting of the AMERICAX (?HEJfICAL SOCIETY (6). By “unit processes” we mean the commercialization of a chemical react’ioii under such conditions as to be ecoiiornically profitable. This naturally includes the machinery needed and the economics involved, as well as the physical and chemical phases. Rut here we lay stress upon the chemical changes and upon the equipment and conditions necessary to effect these changes economically in distinction from the unit operations involving specifically the physical changes. Many have not liked this nomenclature of unit processes; James R. Kithrow, of Ohio State University, prefers “chemical processes”, and the writer made the suggestion some gears ago ( 2 ) that “unit ~iroc:edures”might be better. However, the term “unit processes” is fully entrenched in the literature and has the backing of the American Institute of Chemical Engineers; the presumption is that we shall continue calling this phase ( i f our chemical engineering “unit processes”. The American Institute ( i f Chemical Engineers now defines “chemical engineering;” as follows ( 7 ): “Chemical engineering is that branch of engineering concerned with the de\-elopment a i d application of manufacturing processes in which chemical or certain physical changes of materials are involved. These processes may usually be resolved into a coordinated series of unit phj$cal operations and unit chemical processes. The work of the chemical engineer is concerned primarily with the design, construction, and operation of equipment and plants in which series of these unit operations and processes are applied. Chemistry, physics, and niathe-
T
T h e papers which follow (pages 147 t o 183) were presented a s a symposium on Unit Processes before t h e Division of Industrial and Engineering Chemistry a t t h e 98th Meeting 01 the .imerican Chemical ‘Society, Boeton, >lass.
145
matics are the underlying sciences of chemical engineering, and economics its guide in practice.” These unit process symposia are participated in by teachers and industrialists. This classification helps both in many ways, particularly by ljringing together under the dozen or so main heads of the unit processes a great number of otherwise isolated facts and principles. By grouping oxidation reactions, for example, under the unit process of oxidation, a co~isiderable amount of order is brought into these reactions. Thus, similarity in apparatus can be treated and likewise similarity in principles, with the enhancement in ease of application that such a scientific arrangement brings. From the viewpoint of the teacher particularly, student interest is considerably increased by this grouping of like procedures. The student sees order among what otherwise would be a heterogeneous presentation of numerous individual processes. hIany teachers present to their students industrial processes by the “case system”. Although this case system works exceedingly well, particularly if the presentation is on the basis of flow sheet’sillustrated by lantern slides of equipment and the like, the arrangement of all cases involving nitration reactions under nitration as a unit process brings like principles and apparatus together. By thus arranging like procedures under a given unit process, things that are related become so apparent that many can be handled in the first example given under a unit process, with a simple reference to this for the other procedures presented. The writer’s experience, both in classroom and in reference books, indicates that a certain flow sheet, inirolving the fundamental chemistry, the equipment, and the economics, can he selected to illustrate a given point which is t,he outstanding characteristic of this particular procedure. For instance, in discussing under oxidation the manufacture of phthalic anhydride by the vapor-phase oxidation of naphthalene, the accurate temperature control necessary for high yields in this reaction is described by depicting the Downs mercury reactor.
INDUSTRIAL AND ENGINEERING CHEMISTRY
146
A similar close temperature control is necessary in other oxi dations-for instance, in making maleic acid from benzene. It would clearly not be necessary to do more than mention this fact under the second example. This unit process classification also makes principles of more value for the practicing chemical engineer. For, nlthough a man may actually never be busied in his industrial experience with the particular examples of the oxidation unit process that he learned in college or from his past experience, yet the chemical engineer may take the general principles enunciated and specifically illustrated, and apply them as the ha+ for the study of a new oxidation reaction. This is true not only of manufacturing but also of research and development. The unit process classification also parallels actual factory operations in many instances; rre have all seen a building given orer to diazotization and coupling reactions, or largely occupied by esterifications or nitrations. One large company in a single plant hydrogenates nitrogen to ammonia, carbon monoxide to methanol and higher alcohols, and fatty acids to various products. Both organic and inorganic chemical reactions may well be arranged under the same unit process. While discussing oxidation, the making of sulfuric acid can be presented along with phthalic anhydride. If it is thought best to keep the inorganic and organic divided, a t least under the procedure necessary to control the organic reaction, it should he stated that in the oxidation of sulfur dioxide to trioxide the same careful design of equipment is required to secure the temperatiire control requisite to good yields.
TABLEI.
Typ1c.41.
C0S.I' DISTRIBUTIOS OF
CHEMICALS~
riniline from
Sitrobenzene Reference Total cost of raw materials General expenses (administration, insurance, fixed charges, depreciation) Labor and maintenance (supplies. repairs, direct supervision, and all other operating costs) Fuel and power (steam. air. water, brine. electricity: Total plant cost Cost distribution, % ' Raw materials General Labor and maintenance Fuel and power
Nitrobenzene
SEVERAT. O R G A S I C
.icetic .Icid (Glacial) Alade from Arerat,e of Lime
(4 )
(3'
(1I
$9.23
$4.72
$0.50
$5.Sl $0 52
$1.00
$0.13
$0.80
s0.20
$0.16
$11.52
$6.68
$3.86
80.1 4 3 8.i 6.9
87 0 i.8 2.2 3 0
80.3 1i.5 , .4 2.8
50.67
=Figures given on basi? of 100 pounds of producr and quoted to t h e nearest whole cent.
We who have been responsible for the manufacture of chemicals would like to have available definite formulas to ascertain the cost of carrying out any chemical reaction. Our only possible approach to such a Vtopia 1s gradually t o accumulate related facts and principles in a given narrow field from which we may hope some day t o lay clown some useful formulation regarding the conduct of each unit process. 81ready, thanks to the physical chemist, we are accumulating much data on the chemical energy changes and learning how, in some instances, to predict the course of chemical reactions. The unit process classification, together with the unit operation data, are steps toward this goal. The chemical aspects of manufacturing chemicals covered by unit processes are fundamental to the yields and hence
VOL. 32, NO. 2
TABLE11. TYPICAL COSTDISTRIBCTION OF SEVER.IL INORGAKIC CHEMICALS' 98%
100% HIJOI.
Contact Process Reference Total cost raw materials General espense (administration, office, research, sanitation, hosqital, taxes, depreciation, insurance, etc.) Jlaintenance [ l a b o r and supplies for upkeep and repairs'
Caustic Soda, Phosphoric Acid Lime-Snda fPpOi) (from OilProcess Burning Furnace)
(1)
(1)
(r9)
$0.42
60.9i
$0.92
$0.09
$0 23
$0.22
$0.03
$0.10
Included under general expense
Labor
$0. 04
$0.15
$0.15
Fuel and power
$0 03
Total plant cost Cost distribution, % Raw materials General 1Iaintenance Labor Fuel and power
$0 61
60.21 61.66
$0.53 $1.82
68.9 14.4 5 .0 6.5 5.2
58.6 13.6 6.1 8.9 12.8
60.6 12.1
...
8.2 29.1
a Figures given on basis of 100 pounds of product and quoted t o nearest whole cent.
the costs. Tables I and I1 indicate this importance by the high percentage the chemical raw material bears to the total plant cost. They were compiled from information found in references I , 3, 4,and 8. I n each case the information was altered to conform to the general arrangement of the tables. The figures in reference 1 are given as percentages of the average selling price for 1932. These percentages were recalculated, excluding the cost of distribution and profit, and expressed as percentages of the total plant cost (production cost). The dollars and cents figures from this reference were obtained from the original percentages and the 1932 market price of each chemical. I n these chemicals the yields are excellent, mostly above 90 per cent. I n many manufacturing procedures, especially new undertakings, the chemical yields are lower than these figures show, These tables indicate the great influence that w e n a one per cent increase in yield will hare upon decreasing the costs, by taking one per cent of the material cost of any of the items presented and subtracting it from the total cost. S o operating superintendent will pass over this chemical yield lightly. As the tables show, the cost of the raw materials looms up in the cost distribution. We should emphasize this phase of our chemical industry as its most important and fundamental aspect. All this exemplifies the need for the study of chemical changes and of the equipment for commercializing themnamely, unit processes. May future research bring more order and formulation into this field, and encourage research publication in all phases of unit process! Such is the function of these symposia. Literature Cited (1) rinon.. Chem. d- . l i e f . Eng., 39,2-3 (19321. (2) G e r m a n n . F. E. E., IND. ENG.CHEM.,N e w s E d . , 10, 218 (1932). (3) G r o g g i n s , P. H., " . h i l i n e a n d Its D e r i v a t i v e s " , p p . 95-6, N e a York, D. V a n X o s t r a n d Co., 1924. (4) Groggins, P. H . , " U n i t Processes i n Organic S y n t h e s i s " , 2 n d ed., p . 106, X e w York, McGraw-Hill Book Co., 1938. ( 5 ) ISD. ESG.CHEM.,24,1091-1109, 1285-75, 1344-68 (1932). (6) I b i d . , 29,1329-64 ( 1 9 3 7 ) ; 31,251-82 (1939). (7) N e w m a n n , -4. B., Trans. A m . Inst. Chem. Engrs., 34,6-7 (1938). ( 8 ) W a g g a m a n , W.H., a n d E a s t e r w o o d , H. W.. " P h o s p h o r i c .4cid, P h o s p h a t e s , a n d Phosphatic Fertilizers", p. 255, New York. C h e m i r a l C a t a l o g Co., 1927.
